In recent years, sipes having three-dimensional shapes, micro grooves, etc., have been employed for the tread patterns of winter tires in order to further enhance their properties, and the tread patterns has been getting fine. Tire vulcanization molds for vulcanizing such winter tires have sectors having molding surfaces, on which thin molding blades for molding the three-dimensionally shaped sipes and micro grooves are provided. Therefore, if cleaning is done according to a shot blasting method which cleans the molding surface of the sector by blowing plastic beads over it, a jet cleaning method with high pressure which cleans the molding surface of the sector by jetting highly pressurized water against it, or the like, a problem is that the molding blades are damaged, the shot blasting method and the jet cleaning method having conventionally been used for cleaning of the molds. As a result, there has been employed for such tire vulcanization molds a plasma cleaning method which is less in physical damage.
Conventionally, an apparatus for cleaning a tire vulcanization mold as shown in FIGS. 3 and 4, for example, is known as an apparatus which performs such plasma cleaning. This cleaning apparatus includes a cleaning tank 101 for putting therein sectors 20 of a tire vulcanization mold for molding the tread portion of a pneumatic tire, pressure reduction means 104 having a vacuum pump 102 for making negative pressure in the cleaning tank 101, a filter 102 and the like, and supply means 105 for supplying a reaction gas Q to the cleaning tank 101. A discharging upper electrode 108 and an electrode table (lower electrode) 109 are disposed in the cleaning tank 101, the upper electrode being connected to a high-frequency power source 107 via an impedance-matching device 106.
The above cleaning apparatus is designed such that sectors 120 are put on the electrode table 109, the reaction gas Q is supplied to the cleaning tank 101 by the supply means 105 in a state where negative pressure is produced inside the cleaning tank 101 by the pressure reduction means 104, plasma Z is created between the upper electrode 108 and the molding surface 120a of each sector 120 in the reaction gas atmosphere by discharging from the upper electrode 108, and dirt attached to the molding surface 120a of the sector 120 is removed by a chemical reaction of the reaction gas Q and plasma discharging (see a patent document 1, for example).
Plasma cleaning by the above-described apparatus, however, takes a longer time to clean them, compared to the conventional cleaning methods such as a shot blasting method. Particularly in the case of a vulcanization mold for winter tires which is very dirty, plasma cleaning treatment must be performed at least twice. As a result, cleaning time greatly increases, and a problem is that cleaning efficiency is substantially lowered.
Patent Document 1: Japanese Patent Application Kokai Publication 2001-293729